This invention relates to improvements in a lubricant composition, and more particularly to the lubricant composition containing diamond nano-particles, applicable to a sliding section or sliding member of an automotive internal combustion engine or power transmission apparatus to significantly lower a friction coefficient.
Global environmental problems such as global warming and ozone depletion are coming to the fore. As it has been said that the global warming is significantly affected by CO2 emission, and therefore reduction of CO2 emission has become a big concern to us. To enhance vehicle fuel economy in order to reduce CO2 emission is one of contributions to such problems. Therefore, the development in various technologies has been advanced, for example, a technology of reducing mechanical loss of an internal combustion engine.
There are proposed the following approaches to reduce mechanical loss due to a lubricating oil (or lubricant): (1) lowering the viscosity of the lubricating oil, thereby reducing viscous resistance in hydrodynamic lubrication regions and agitation resistance in the engine; and (2) adding a suitable friction modifier and other various additives into the lubricating oil, thereby reducing friction losses under the conditions of mixed and boundary lubrication. In view of the foregoing, many studies have been made on various friction modifiers mainly including organic molybdenum compounds such as molybdenum dithiocarbamate (MoDTC) and molybdenum dithiophosphate (MoDTP). There are disclosed in Japanese Patent Provisional Publication No. 8-20786, one of the above-mentioned studies, to employ a lubricant that contains an organic molybdenum compound imparting an excellent low-friction coefficient to conventional steel sliding members in the early stage of usage, which successfully provides a friction reducing effect to a certain extent.